Abstract: Cytomegalovirus (CMV), Human Herpesvirus-6 (HHV-6), belong to the ß-herpesvirus subfamily. These viruses can be reactivated from latency during immunosuppression. period especially after liver transplantation, CMV has been the most important opportunistc infection that negatively influences the outcome of patients. HHV-6 is a lymphotropic virus, but it may also infect other cells, such as monocytes and epithelial cells, using the CD46-molecule as a cellular receptor. HHV-6 reactivations are often seen associated with CMV infection and allograft rejection. In liver transplant patients, HHV-6 reativations are frequently found together with CMV infection. CMV has been implicated as an important causes of morbidity and mortality among solid organ transplant patients. Both have been related to graft dysfunction, bone morrow suppression, and predisposition to CMV disease. In this study, CMV and HHV-6 DNA were detected in 41 liver transplant patients, using nested polymerase chain reaction (PCR). This method was chosen because increase the sensibility and with the products we can be classified into CMV genotypes. We also evaluate the co-infection and the clinical impact between those virus in liver transplant patients. 145 biopsies were tested, (41 - liver donor biopsies and 104 - liver post- transplant), Twenty three (15,8%) of 145 liver biopsies were CMV- PCR positive and fifty three (36,5%) of 145 were positive HHV-6- PCR. Nineteen (13%) of 145 biopsies were both CMV and HHV-6 positive. 21 patients had allograft rejection and 16 had infection for this virus. With the presence of the viruses observed in the samples of the donor and post-transplant, suggests that pre-transplant HHV-6 and CMV infection may be a risk factor post-transplant. They had associated with allograft refection.